It takes a huge mistake, as compared to other pistol calibers, to reach too high of a pressure in a .45ACP.
It can be done, though.
If you choose a powder that fills the case pretty good, for a normal charge, it isn't likely to happen.

Accuracy - Accuracy is best at certain pressure nodes. Usually 1 at near min charge weight and one at near max. So, when working up a load, bad accuracy is a sign.

Velocity - If you have a 230gr 45 ACP load running 1000 fps, it is likely TOO hot. 850 is std hardball, 770 softball, 900 warm, 950 is +p sd ammo in general. This varies by powder. Know what too fast is for your powder.

Sd - Standard deviation when working up a load. This normally get it's best at max safe load, then opens up. Bigger numbers near max manual charge indicate the load is too hot. Usually, I get an ok sd at min, then it gets worse, then while approaching max, sd becomes the smallest. Over max, it gets bigger again.

Recoil - Factory ammo is nearly all max pressure or over in the case of +p. If your loads recoil more than factory fodder, it probably is too hot.

Primer Drag - on many guns, hot loads have some primer tip drag against the primer. Some is ok. Learn how this looks on factory ammo and set that as a visual max.

Primer reading - low pressure primers can be read too. Look at the edge before and after firing. Compare to same brand factory ammo for max limit. Also look in the tip dent. Look at the way the pin tip radius gets pushed out of the primer by the anvil. That is a key pressure sign.

Also, there is:
low pressure
safe pressure forever
safe pressure for a few thousand rounds, but will ultimately break something +p
safe pressure for a few rounds, but really is a proofing load
unsafe and part of your barrel is in your safety glasses and your mag shot out so hard it dented your steel toes!

I have worked up 45acp in a rifle until the primer fell out.
That is way up there ~ 60 kpsi.

But in a semi auto pistol with a reasonable slide mass and a reasonable recoil spring force, the recoil should stop the work up before 20 kpsi.

Before 20kpsi is reached, the cases should be landing at least 5 feet away and the slide should start hammering the frame.

20 kpsi pressure, there is nothing to see.

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If you see a ruptured barrel in .45 ACP, or a case-head separation that wasn't due to overly fatigued brass (which isn't common with .45 ACP) it is almost certainly due to at least a double-charge of powder.

There are a good number of powders, particularly dense sphericals that can be double-charged in the .45 ACP case, so attention to detail is very important, but that's the case for any cartridge you handload.

For high velocity JHP loads I use Silhouette. It can be double-charged, but that would prevent you from being able to completely seat the bullet. www.ramshot.com provides data and they have a load with a 185 gr. XTP that achieved 1152 FPS with Silhouette at just below 21,000 PSI, so it is still a standard pressure load, but runs just a hair faster than the Remington 185 gr. +P Golden Saber factory load. I mention that because I use the Golden Saber in my 185 gr. handloads with Silhouette.

The pressure rating for +P is 23,000 PSI which is still relatively mild pressure as far as defense handgun cartridges go. There is nothing about the slightly higher pressure that makes recoil objectionable for me firing the loads in polymer framed pistols. Recoil is subjective to the individual shooter. Recoil is a product of the bullet's weight and velocity, so pressure is only relative in the fact that +P loads may go up to the 23,000 PSI SAAMI pressure rating.

For most semi-auto pistol rounds, the best indicators I have found are recoil and distance case are thrown compared to factory loads with the same weight bullet.
Many .45s have a LOT of unsupported case (feeding reliability vs case support, with the low pressure making them think that case support is not needed), so any bulging is also sure sign you are OVER pressure.
I always wondered about magazine writers who warn that XXX cartridge is made with thin case walls and won't hold pressure. If the case is supported properly, all the case knows is pressure on one side and solid steel on the other and thickness doesn't matter. Thus, I always figured it was the strength of the cylinder/gun and NOT the strength of the .45 Colt case that limited pressure.

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